In many surgical operations work must be done on a moving organ, such as a beating heart. This requires not only manipulations to perform the operation which would be required in any case (even if the organ were still), but also requires correction of the surgeon's hand motions to compensate for the organ motion so as to keep the surgeon's hands still relative to the work area.
One such operation which has recently been gaining in popularity is known as minimally invasive coronary artery bypass grafting. As described by Calafiore et al, "Minimally invasive Coronary Artery Bypass Grafting", Ann. Thorac. Surg., 62:1545-1548 (1996), minimally invasive coronary artery bypass (MICAB) is defined as an intervention that does not require median sternonomy or the use of cardiopulmonary bypass (CBP). The incision in the chest wall is small, and the aorta, in any portion, is not the direct source of inflow of blood supply to the bypass grafts. MICAB promises to become an important addition to the surgical treatment of coronary artery disease.
In this technique, the patient is anesthetized and intubated with a single endotracheal tube and hemodynamic monitoring. Short-acting anesthetic agents are used, as extubation of the patient in the operating room is routine. The chest is opened through a fourth or fifth intercostal space incision and the pericardium is opened longitudinally. The left anterior descending coronary artery (LAD) is identified and inspected. The LIMA is harvested through the same incision with or without the aid of a thoracoscope. One or more costal cartilages may be resected to achieve better visualization and dissection of the full length of the LIMA. The artery can be harvested as a pedicle or as a skeletonized vessel.
The patient is heparinized (1 mg/kg), and diluted papaverine is injected into the pedicle and intraluminally into the LIMA through a blunt-tipped cannula. Traction sutures are applied to the edges of the pericardium. After selection of a site for construction of the anastomosis and assessment of the length of the LIMA, distal and proximal control of the LAD is required. A snare of 4/0 PROLENE (Ethicon, Somerville, N.J.) or silicone suture can be applied proximally and distally to the site selected for the anastomosis. Alternatively, the vessel can be opened and a FLOW-RESTER placed intraluminally. The surgical blower (VISUFLOW, Research Medical, Midvale, Utah) is used for visualization. Electrocardiographic changes, arrhythmias, and ventricular fibrillation are rare events during occlusion of the LAD. Traction sutures can be applied to the visceral pericardium lateral to the LAD, thereby allowing for better stabilization of the artery. Alternatively, a suction device (Medtronic Inc, Minneapolis, Minn.) or a stabilizer (CTS Inc) can be used. Short-acting .beta.-blockers or calcium channel blockers are used to reduce heart rate when necessary.
The LAD to LIMA anastomosis is performed using a 7/0 or 8/0 running PROLENE suture, either as a single suture or as two strategically placed sutures at the toe and heel of the LIMA. Some surgeons prefer interrupted sutures. At completion of the anastomosis, heparin is reversed with protamine sulfate. Closure of the chest is as in any standard thoracotomy, leaving a pleural tube for drainage. An intrapleural catheter is placed for pain control. The patient is extubated in the operating room or shortly thereafter. Patency of the artery is confirmed by standard Doppler (velocity) echocardiography intraoperatively and by duplex scanning of the LIMA early and late postoperatively in every patient. This is usually done 2 to 3 hours postoperatively and 24 hours after operation. Diastolic flow predominates in a patent LIMA. Most centers report early discharge from hospital and significant cost savings associated with this procedure.
It has been reported that by mid-1996 at least 200 MICAB procedures had been performed in various universities and private hospitals in the United States and several hundred more in Europe and South America (Hartz, "Minimally Invasive Heart Surgery", Circulation, 94:2668-2670 (1996)). For other respects about such surgery, see also Calafiore et al, "Left Anterior Descending Coronary Artery Grafting Via a Left Anterior Small Thoracotomy Without Cardiopulmonary Bypass", Ann. Thorac. Surg., 61:1659-1665 (1996); Stanbridge et al, "Minimal-Access Surgery for Coronary Artery Revascularization", Lancet, 346:837 (1995); Acuff et al "Minimally Invasive Coronary Artery Bypass Grafting", Ann. Thorac. Surg., 61:135-137 (1996), and Subramanian et al "Minimally Invasive Coronary Artery Bypass Surgery: A MultiCenter Report of Preliminary Clinical Experience", Circulation, 92 (Suppl. 2):645 (1995).
While such operations have been successfully performed in many different centers, substantial risks are involved in performing surgery on a beating heart. In such operations the arteries are small, the stitches fine, and the sutures are liable to rip due to the heart motion. The risk to the patient is considerable. There have been cases in which the arterial walls were ripped, requiring the operation to be aborted and causing complications.
At first blush it might appear that the heart's motion, being regular, could be easily compensated for by the surgeon. However, the heart motion amplitude is about a half inch (1.3 cm), and this is quite large compared to the precision required of the surgeon's manipulations. The rhythm is erratic. The motion tends to sudden pulsations rather than a smoothly-varying motion such as a sinusoidal motion.
Thus, the acceleration of the heart surface changes rapidly. During the intervals of high acceleration the surgeon is substantially unable to do anything beyond keeping the instruments near their positions relative to the heart, so that no suture rips or unintended punctures occur. The operation is actually performed intermittently during the lulls of low acceleration.
Because of these difficulties, the heart is often artificially slowed down during operations, as discussed above, such as by means of short acting .beta.-blockers or calcium channel blockers. This improves the surgeon's situation in proportion to the change in rate, but for obvious reasons the degree of improvement is limited.
Moreover, the heart (like most organs) responds to stimulation. A suture needle prick often causes this muscular organ to twitch strongly, which is very difficult to compensate for. Twitching will not be lessened by slowing the heart down.
Calafiore et al, supra, report that stabilization of the heart during construction of the anastomosis is an important aspect of the procedure, and devices are being developed that will aid the surgeon during this critical part. However, physically immobilizing the heart is a less than desirable technique as it could damage the heart or impair circulation during this period.
Devices for surgery on a beating heart were reported in a front-page story in the Wall Street Journal of Apr. 22, 1997. The story said that CardioThoracic Systems, Inc. is marketing a device resembling a two-pronged fork which is pressed against the beating heart to stabilize the pressed region and allow the surgeon to operate. The cost is $1850 per operation. Another device sold by Medtronic is called the "Octopus"; it costs $10,000. Others are expected to be marketed soon by Baxter Inc. and U.S. Surgical Corp.
The CardioThoracic system can only be used in about 20% of all bypass operations, according the article. Triple and quadruple bypass and valve repairs require stopping the heart.
Pressing on the heart naturally will affect the blood flow through it, and the amount of pressure is limited. The problem of twitching is not overcome, and it appears that the heart surface cannot be immobilized completely.
The new devices "set off intense debate over safety and economics", according to the article. "Some surgeons are particularly skeptical that joining tiny blood vessels on the surface of the heart can be done as successfully while the heart is beating--the CardioThoracic way--as when it is stopped. . . . During a recent stopped-heart! operation, Dr. Colvin of New York University Medical Center! peered through magnifying goggles as he performed the delicate task of joining the replacement vessel to a coronary artery, using a tiny needle and barely visible sutures. `At this point, if you're doing it "beating-heart" you're cursing a mile a minute`, he remarked."
The article also reported on a stopped-heart kit which is being aggressively marketed in competition with the CardioThoracic device. Produced by Heartport Inc., is! it costs $5000 per kit. It has been used in about 500 cases. Like the CardioThoracic method, the Heartport method avoids opening the ribcage, instead using a smaller opening. Because opening the ribcage is a traumatic and painful operation, patients are more likely to chose an operation which requires only a smaller opening.
However, the Heartport method involves stopping the heart with a balloon in the aorta and drugs, and using a heart-lung machine to keep the patient alive during the operation.
The article noted that stopping the heart is stressful and dangerous, and is impossible if the patient is too sick. The cost of using the heart-lung machine is as much as $2,300 (the machines cost about $150,000) and about 6% of patients suffer complications, including stroke, depression, and severe infections. The ideal heart operation would need only a small incision, like the Heartport and CardioThoracic operations; avoid the expense and risk of a heart-lung machine, like the CardioThoracic operation; and stop the heart so the surgeon can safely operate on the delicate arteries, as in the Heartport operation. None of the available operations or devices achieve all these.
The prior art has not solved these problems of working on a moving organ, despite the great need for improvement.